1. Field of the Invention
The invention is directed to an arrangement for the polarization of light, preferably for use in projectors, with at least one illumination source, an integrator with a light entrance plane and a light exit plane which serves to homogenize the unpolarized light bundle proceeding from the illumination source and/or illumination sources, a structural component part which has the entrance opening and which is constructed so as to be reflecting in the direction of the interior of the integrator, and the intensity maximum of the light bundle propagates along an axis extending between the light entrance plane and the light exit plane, the surfaces formed so as to be reflecting for guiding the light bundle, and means for the polarization and reflection of partial beams of the light bundle.
2. Description of the Related Art
Known arrangements for the polarization of light, or polarization recovery systems as they are called, are located in the illumination beam path of unpolarized light sources and are applied chiefly where high illumination intensities of polarized light are desired or a particularly efficient use of the light exiting from the light source is required for the overall polarization state. In this connection, the usable polarized proportion of lamp light output must be increased to more than 50% of the total unpolarized light output.
Since this can not be implemented using conventional polarizers, e.g., birefringent crystals or polarizing sheets, prism arrangements which split the unpolarized light into two components that are polarized vertical to one another are being used to an increasing extent. The light proportion that is not polarized is subsequently rotated in the required direction by means of at least one phase plate and is added to the proportion that has already been polarized in the desired direction. Depending on the embodiment form, the condenser constant of the illumination doubles.
Polarization recovery systems are frequently used in projectors based on transmissive LCDs. They mainly have a construction similar to a honeycomb condenser, the second honeycomb plate is located near the first honeycomb plate and a raster or grid of many prism arrangements is provided instead of element lenses. The function of polarization recovery is thus linked to the improvement in the uniformity of light. Further, while they bring about an efficient use of large light sources with particularly high light output, the increase in the condenser constant being secondary, they are disadvantageous in that their construction is very complicated and the entire system is accordingly cost-intensive.
New reflective LCDs (LCOS) also require linearly polarized light for their operation. Since they are considerably smaller than the transmissive LCDs, they also need lower condenser constants in part. Further, special color management systems whose characteristics additionally limit the condenser constant are required in LCOS of the type mentioned above, for example, in 3-chip arrangements.
Under these circumstances, polarization recovery systems of the type described above can only be used to some extent, since either the light efficiency is considerably lower than in transmissive LCD systems or only special light sources delivering a low light output themselves can be used.
At Electronic Imaging 01/2002, San Jose, Calif. USA, M. Duelli, T. McGettigan (OCLI-A JDS Uniphase Corporation) and C. Pentico (Advanced Digital Optics) presented a polarization recovery system which uses a solid integrator (light mixing rod) whose light entrance element has a reflecting surface facing in the direction of the interior of the integrator and in which a reflective polarizer is arranged in the exit plane.
The light falling into the integrator via the light entrance opening is mixed by total reflection in the integrator and reaches the reflecting polarizer. While the transmission-polarized portion of the light exits the integrator through the polarizer, the light component that is not transmission-polarized arrives back at the inner surface of the light entrance element, is reflected there and is homogenized again when it passes through the integrator again. Quarter wave plates are arranged in the integrator in addition for rotating the polarization direction of the light beams. The transmission-polarized component passes through the polarizer again and is added to the light that is already transmission-polarized. This process is carried out until the light component in its entirety, with the exception of the absorbed partial beams and reflection losses, has been polarized in the desired direction and exits from the integrator. Quarter wave plates are additionally arranged in the integrator for rotating the polarization direction of the light beams.
Arrangements of this type have the advantage that the condenser constant is increased only in the ratio of the exit surface to the entrance surface of the integrator.
On the other hand, it is disadvantageous that a quarter wave plate for rotating the polarization direction is to be arranged in the interior of the light mixing rod (solid integrator) and must pass through the latter repeatedly.